1. Field of the Disclosure
Embodiments disclosed herein relate generally to methods and apparatuses to monitor solenoid actuator movement. More particularly, embodiments disclosed herein relate to methods and apparatuses to monitor solenoid actuator movement through current monitoring.
2. Related Art
In sub-sea electrical/hydraulic pressure control systems used, for example, in a BOP system (blowout prevention system) of a drilling rig, solenoid actuators are used to open and/or close hydraulic paths connected to hydraulic valves which control the mud flow through a wellbore. For example, when unexpected high pressure gases are detected when drilling for oil, a control signal is sent to a solenoid control circuit to close or open one or more critical valves so that mud flow can be blocked to prevent people on a drilling ship or platform from being injured or killed by the uncontrolled flow of high temperature mud. Often times, in such subsea systems, several groups of solenoids are used as control switches. Conventionally, the current passing through a solenoid coil is monitored to determine if the correct current level fed to a given solenoid coil for the opening or closing action of the solenoid actuator. This existing solenoid current monitoring method does not confirm if the solenoid actuator has properly moved or not due to, for example, a mechanical failure.
Conventional solenoid current monitoring circuits include a plurality of channels, each of which may be corrected to an individual solenoid coil connected to a corresponding current sensing element. Usually, the sensing element includes a resistive element (e.g., a simple resistor disposed in series with the solenoid coil), the voltage drop across the resistor being proportional to the current flowing through the solenoid coil. In these conventional circuits, the voltage across the resistor is conditioned and read by an analogue to digital converter (ADC), and this voltage measurement is used to determine a current value for the current passing through the solenoid coil.
Solenoid current monitoring circuits such as the type described above typically monitor and report the value of the current that passes through a solenoid coil after its energizing or de-energizing process is completed. Thus, as already noted, existing control systems report the working status of a solenoid coil without detecting any actual physical movement of the solenoid actuator (i.e., existing methods for monitoring current in a solenoid coil do not detect whether the solenoid actuator actually extends or retracts). Thus, if a mechanical failure occurs on the solenoid actuator, the existing current monitoring circuits may report that the solenoid actuator is “working” because the correct current value may still be detected in the solenoid coil although the actuator may have not moved.
Position sensors or motion sensors may be installed on a solenoid coil to sense the movement of the actuator. The signal from the sensors are fed back to the central system to determine if the solenoid actuator moved according to the control signal. To implement such position and/or motion sensors, the solenoid actuator and its housing must be redesigned mechanically to mount the sensor, and extra wires must be used for power/signal lines to connect to the position and/or motion sensor. In other words, major modifications are necessary to carry out the motion detection of the solenoid coil.